The objective of our research program is the elucidation of the chemical mechanism and of the biological significance of interactions between steroid hormones and proteins of various origins. These will be mainly specific serum proteins of high binding affinity; receptor proteins of target tissues will be included and studied in their relationship to serum binders. The specific aims include studies with: a) Alpha1-acid glycoprotein and corticosteroid-binding globulin to elucidate the chemical structure of the steroid-binding site; b) progesterone-binding globulin of the pregnant guinea pig; chemical nature, binding properties and significance of carbohydrate constituents; c) progesterone receptor protein in the uterus of the pregnant guinea pig and its relationship to the serum binder; relationship of cytosol receptor to nuclear receptor, and their role in the mechanism of progesterone action. The methods used are those applied in the applicant's laboratory for many years, in addition to newly developed techniques.